The invention relates to a method and to an apparatus for improving exhaust gas recirculation in an internal combustion engine, in particular a diesel engine, having an exhaust gas turbocharger.
Recirculating exhaust gases is used as one way of reducing emissions of pollutants, such as, for example, nitrogen oxides NOx, in internal combustion engines. This involves recirculating a portion of the exhaust gases of the internal combustion engine back into its intake system, for example by opening and closing an exhaust gas recirculation valve in a controlled manner. Internal combustion engines, such as diesel engines, are frequently equipped with exhaust gas turbochargers.
However, it is possible when recirculating exhaust gas for states to occur in the transient region in which the exhaust gas pressure is not sufficient for the portion removed via the exhaust gas recirculation system to be conveyed into the intake line or the intake manifold of the internal combustion engine. In such an operating state, there consequently results an excessively high content of NOx in the exhaust gases.
Such internal combustion engines, for example piston machines such as diesel engines, with an exhaust gas turbocharger have, for example, an operating state during acceleration which is referred to as “turbo lag”. Here, when stepping on the gas, the internal combustion engine reacts with a speed increase only after a defined delay period in which no exhaust gas energy, i.e. insufficient exhaust gas pressure, is available for driving the exhaust gas turbocharger, and hence no compressed fresh gas is available. Proposed solutions for overcoming this “turbo lag” have been described in laid-open specifications DE 10 2006 008 783 A1 and DE 10 2006 008 785 A1. They involve introducing compressed air, for example from a compressed air accumulator, into the intake line of the internal combustion engine in a controlled manner in order to cover an increased demand for fresh gas in the internal combustion engine. This takes place by means of a component which is arranged in the intake line between the compressor of the turbocharger and the intake manifold and which comprises a compressed air connection and a controlled flap. The controlled flap is closed when feeding in compressed air, with the result that the compressed air is directed to flow into the intake line rather than into the compressor of the exhaust gas turbocharger.
It is therefore the object of the present invention to provide a method and an apparatus for improving exhaust gas recirculation wherein the above disadvantages are obviated or significantly reduced and further advantages are obtained.
A fundamental idea behind the invention comprises making use of a vacuum for sucking in recirculated exhaust gas, this vacuum being created when blowing compressed air into the intake line of the internal combustion engine.
As a result of this, it is advantageously ensured that the states occurring in transient operating regions of the internal combustion engine where exhaust gases have excessively high nitrogen oxide contents are eliminated or considerably reduced.
A method according to the invention for improving exhaust gas recirculation in an internal combustion engine, in particular a diesel engine, having an exhaust gas turbocharger comprises the following method steps: determining operating parameters of the internal combustion engine in order to determine pressure values of the exhaust gas; controlled feeding of compressed air based on the pressure values thus determined for the exhaust gas in order to generate a vacuum in a feed section of a gas feed device; sucking a portion of exhaust gas of the internal combustion engine into the feed section of the gas feed device with the vacuum generated; and recirculating the thus sucked-in portion of the exhaust gas into the internal combustion engine via an intake line connected to the gas feed device.
The compressed air is blown in at a high pressure via a controlled valve, for example a solenoid or pneumatic valve. Here, very high flow viscosities, preferably equal to the speed of sound, of the blown-in compressed air occur directly behind the outlet of the valve in a small region. In this region then prevails a considerably lower pressure than in the intake line of the internal combustion engine.
In a further embodiment, it is preferred to design this region as a venturi arrangement, with the result that the vacuum produced is particularly pronounced. In this vacuum region, the portion of recirculated exhaust gas is sucked in by the vacuum. As an alternative, use can also be made of an injector pump arrangement.
Particularly when the internal combustion engine is in an operating state in which the exhaust gas pressure is low, compressed air is blown in while exhaust gas that is to be recirculated is sucked in. The compressed air valve is switched on when pressure values of the exhaust gas, which are measured directly or indirectly, fall below a predefinable value. Then, the vacuum builds up and a recirculating valve in the exhaust gas recirculation system is switched on to open it such that the portion of exhaust gas that is to be recirculated is sucked in.
The sucked-in exhaust gas that is to be recirculated is blown together with the compressed air into the intake line of the internal combustion engine. To ensure that the compressed air and the sucked-in exhaust gas can be directionally guided into the intake line, provision can be made for a setting element which directionally steers the flow into the intake line.
An apparatus according to the invention for improving exhaust gas recirculation in an internal combustion engine, in particular a diesel engine, having an exhaust gas turbocharger, comprises the following: an exhaust gas recirculation device which is connected to an exhaust gas line and to an intake line of the internal combustion engine; a recirculating valve arranged in the exhaust gas recirculation device and intended for the controlled switching on of exhaust gas recirculation; and a gas feed device which is arranged between the intake line and a compressor of the exhaust gas turbocharger and coupled to a compressed air line, wherein the gas feed device further comprises an intake duct with a connection for the exhaust gas recirculation device, and wherein the intake duct leads into a feed section of the compressed air line.
Provision is made in a preferred embodiment for the gas feed device to comprise, upstream and downstream of the setting element in the flow direction, measuring devices for measuring flow parameters in the gas feed device. This makes it possible in a simple manner to obtain measurement values, for example, on the current intake pressure in the intake line, the measuring devices being pressure sensors, for example. The intake pressure and further measurement values, for example from the engine control unit, such as the speed of the internal combustion engine, can be used to infer the exhaust gas pressure as well.
In a further embodiment, the gas feed device is a fresh gas line section of a device for fresh air supply for blowing in compressed air in a controlled manner. This gives a combination of the advantages provided by blowing in compressed air in terms of the so-called “turbo lag” and the improved exhaust gas recirculation.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of one or more preferred embodiments when considered in conjunction with the accompanying drawings.
Identical components or functional units having an identical function are designated by identical reference signs in the figures.